1. Field of the Invention
The present invention relates to a bismuth-zirc-niobnate pyrochlore thin film, abbreviated as xe2x80x9cBZN,xe2x80x9d represented by the formula:
(Bi3xZn2xe2x88x923x)(ZnxNb2xe2x88x92x)O7
wherein x is fro m about 0.45 to about 0.73. More particularly, the present invention relates to a process of preparation of such thin films and coated articles that are suitable for use in dielectric applications.
2. Description of the Prior Art
The rapid development of communication technologies, especially mobile communication systems, has been greatly facilitated by miniaturization of devices used in such systems. Integrated decoupling capacitors and microwave resonators are of particular usefulness in such systems. Dielectric materials for these applications must possess a moderate to large dielectric constant, low loss tangent (tan xcex4), high dielectric quality factor Q (Q is equal to 1/tan xcex4), and a small temperature coefficient of resonator frequency (for resonators). Bi2O3xe2x80x94ZnOxe2x80x94Nb2O5 (BZN) pyrochlore ceramics have previously been developed for low firing temperature multilayer capacitors. These are described in M. F. Yan, H. C. Ling, and W. W. Rhodes, J. Am. Ceram. Soc., 73, 1106 (1990), D. Liu, Y. Liu, S. Huang, and X. Yao, J. Am. Ceram. Soc., 76, 2129 (1993), D. P. Cann, C. A. Randall, and T. R. Shrout, Solid State Comm., 100, 529 (1996) and X. Wang, H. Wang, and X. Yao, J. Am. Ceram. Soc., 80, 2745 (1997).
Recent studies by H. Kagata, T. Inoue, J. Kato, and I. Kameyama, Jpn. J. Appl. Phys., 31, 3152 (1992) and S. L. Swartz, and T. R. Shrout, U.S. Pat. No. 5,449,652 (1995) have shown that some compositions of the BZN class also exhibit excellent microwave properties. BZN ceramics with dielectric constants temperature coefficient of resonant frequency |Tf| less than 10 ppm/xc2x0 C. and microwave Qf greater than 5000 GHz have been reported by S. L. Swartz, and T. R. Shrout, U.S. Pat. No. 5,449,652 (1995). Such dielectric properties exhibited by the above BZN system indicate that thin films of this composition may have utility as potential materials for integrated microwave resonators and decoupling capacitors. Thin films may have the advantage of lower crystallization temperatures and smaller device size than bulk ceramics and may be potentially integrated in microelectronic devices.
Fabrication of thin films using Metal Organic Deposition (MOD) techniques have been previously used to deposit dielectric and ferroelectric thin films.
H. -F. Cheng, Y. -C. Chen, and I. -N. Lin, J. Appl. Phys., 87,479-483 (2000) have recently reported Bi2(Zn⅓Nb⅔)2O7 thin films on indium-tin oxide coated glass, deposited by a pulsed laser deposition technique. However, the films prepared by this method have unexpectedly high dielectric constants of up to about 300 and loss tangents of about 2%.
The present invention includes a thin film comprising a pyrochlore represented by the formula:
xe2x80x83(Bi3xZn2xe2x88x923x)(ZnxNb2xe2x88x92x)O7
wherein x is from about 0.45 to about 0.73.
The present invention flrter includes an article comprising a substrate and a thin film comprising a pyrochlore according to the present invention coated on the substrate.
The present invention also includes a process for depositing on a substrate a thin film comprising a pyrochlore represented by the formula:
(Bi3xZn2xe2x88x923x)(ZnxNb2xe2x88x92x)O7
wherein x is from about 0.5 to about ⅔. The process comprises coating the substrate with a precursor composition comprising a bismuth containing metal organic compound, a zinc containing metal organic compound and a niobium containing metal organic compound, an organic solvent, an organic acid and an organic base, heating to remove organic components and annealing at a temperature and for a length of time sufficient to produce the pyrochlore thin film on the substrate.
The present invention further includes a method of depositing on a substrate a thin film comprising a pyrochlore represented by the formula:
(Bi3xZn2xe2x88x923x)(ZnxNb2xe2x88x92x)O7
wherein x is from about 0.45 to about 0.73. The method comprises using a low temperature process comprising a step selected from the group consisting of: sputtering, applying a pulsed laser and depositing by MOCVD (Metal Organic Chemical Vapor Deposition), wherein the step is carried out under conditions sufficient to produce the pyrochlore thin film on the substrate.
The thin films comprising a pyrochlore according to the present invention have properties that include relatively large dielectric constants, small loss tangents, controllable temperature coefficients of capacitance, electric field tunability of the dielectric constant and dispersion of the relative permittivity. These properties make the thin films of the present invention particularly suitable for use in dielectric applications, such as, capacitive components and decoupling capacitors as well as in microwave applications, such as, integrated microwave components. In addition, the process and method of the present invention provide low processing temperatures, precise composition control, uniform deposition over large area substrates and low cost.